1. Field Of the Invention
The invention relates to an improved process for preparation 1,2-benzisothiazole-1,1-dioxides, especially 3-methyl substituted derivatives.
2. The Related Art
Sulfonimines such as 1,2-benzisothiazole-1,1-dioxides have recently been disclosed as bleach catalysts for cleaning fabrics. See U.S. Pat. No. 5,041,232 (Batal et. al.) which discloses 3-methyl-1,2-benzisothiazole-1,1-dioxide Known as SULF-11. The unusually active nature of SULF-11 has focused attention on improved synthetic routes to this material.
Pseudosaccharin chloride in combination with a malonate ester have been reacted to provide the basis for one type of route to these sulfonimides. See articles by Melchiorre, Giannella and Gualtieri, Ann. Chim. (Rome) 61 (6), p. 399 (1971) and Carrington, Clark, Ewes and Scrowston, J. Chem. Soc., Perkin 1, p. 3006 (1972).
A second reported route has involved the reaction of saccharin with two molar equivalents of a Grignard or organolithium salt. This route is described in Abramovitch, Smith, Humber, Purtschert, Srinivasan and Singer, J. Chem. Soc., Perkin 1, p. 2589 (1974) and Hermann, Campbell, Greenwood, Lewis and Wolfe, J. Org. Chem., 57, p. 5328 (1992).
Common to all the references is the underlying assumption that it is necessary to employ a soluble saccharin reactant. Apparently the art as avoided insoluble saccharin reactants that would require a heterogeneous reaction scheme.
Of particular disadvantage in the known art is the use of two moles organometallic reagent. Since organometallic reagents are quite expensive and often pyrophoric, it would be advantageous to limit amounts or these reagents. Furthermore, Grignard reagents of the known art require considerable volumes of solvent. Environmental, cost, safety and other reasons encourage limitation of the solvent volumes.
Accordingly, it is an object of the present invention to provide an improved synthesis of 1,2-benzisothiazole-1,1-dioxides which limits the amount of organometallic reagent necessary for the reaction.
A further object of the present invention is to provide an improved synthesis of 1,2-benzisothiazole-1,1-dioxides which limits the volume of solvent necessary in the reaction.
These and other objects of the present invention will become apparent through the following summary, detailed discussion and examples.